This invention relates to thin film magnetic heads, and, more particularly to a magnetic head having a magnetoresistive read transducer.
The use of a magnetoresistive (MR) sensor to sense magnetically recorded data has been known for many years. It has also been known that both longitudinal and transverse bias must be provided to eliminate Barkhausen noise and to maintain the sensor in its most linear operating range. Commonly assigned U.S. Pat. No. 4,024,489 describes an MR sensor in which a hard magnetic bias layer is used. In this sensor both the MR layer and the hard magnetic bias layer extend across the entire sensor to produce a transverse bias.
Commonly assigned U.S. Pat. No. 3,840,898 discloses an MR sensor in which a transverse bias is produced. In the embodiment shown in FIGS. 4 and 5 a magnetoresistive stripe such as NiFe is treated in edge regions to produce a hard magnetic state. However the edge regions are arranged parallel to the direction of sense current and run along the entire stripe to produce a transverse bias and would not produce longitudinal bias.
It has become increasingly difficult to produce MR read transducers in the small size needed to read the data recorded on ever decreasing track widths at ever increasing recording density. One solution proposed to meet these requirements is described in commonly assigned U.S. Pat. No. 4,663,685 in which transverse bias is produced in only a central active region of the sensor and longitudinal bias is produced in the inactive end regions by means of exchange coupling between the part of the ferromagnetic MR layer which extends into the end regions and antiferromagnetic layers which extend over only the end region. U.S. Pat. No. 4,639,806 shows an MR sensor which has longitudinal bias produced by exchange coupling between the MR layer and hard magnetic layers in the end regions only.
These sensors have been shown to meet the present requirements. However, to meet future design requirements, the dimensional accuracy required severely limits the ability to build these structures in processes that are both economical and sufficiently accurate.
None of the known prior art references disclose an MR sensor in which the MR layer extends over substantially only the central active region and a hard magnetic bias layer is provided in each end region which forms an abutting junction with the MR layer to produce longitudinal bias in the MR sensor.